When image information in surroundings is picked up with a small number of cameras, wide-angle optical systems having a large angle of view for taking images (wide angle of view) are employed in general. For example, such the wide-angle optical system has been used for the purpose of a surveillance system and onboard system.
Further, an onboard camera for monitoring rear view of a vehicle, for example, has been required to be more compact in addition to have a wide angle of view from a viewpoint of a practical use to keep the visibility of a driver and a viewpoint of a beautiful appearance of the vehicle.
Such the wide-angle optical systems are disclosed in Patent Literature 1 and Patent Literature 2, for example. The wide-angle optical system disclosed in Patent Literature 1 prevents shading that is a problem caused when the optical system has a super wide angle and is formed of a small number of lenses such as about four or five lenses. The wide-angle optical system disclosed in Patent Literature 2 controls fluctuations of an image forming position under various temperature environments by employing glass members arranged at proper positions.
Patent Literature 1: JP-A No. 2005-227426
Patent Literature 2: JP-A No. 2007-101920